It was previously observed that injection of rabbits with a human T cell line infected with HIV-1 causes seroconversion within four weeks of injection. In the present studies, we have used the polymerase chain reaction in order to detect viral sequences in cells and organs from infected rabbits at various time points following the single injection that causes HIV-1 infection. In one group of rabbits, animals were sacrificed at two week intervals following infection and various lymphoid and other organs were taken, DNA was isolated and monitored for the presence of sequences from the gag and env regions of HIV-1. In other experiments, animals were superinfected with HTLV-1 approximately one year after HIV-1 infection and peripheral blood and lymphoid organs were monitored at various time intervals following the super-infection event. Results thus far show that animals sacrificed two weeks after injection are negative in all organs for HIV-1 sequences. After four weeks, the spleen is the most likely organ to be positive for HIV-1 followed by lung and appendix. The liver is least likely to be positive. DNA isolated from peripheral blood lymphocytes taken from animals prior to 10 weeks post-infection was almost always negative for viral sequences. After this time, there was the higher likelihood to detect virus. In other studies, brains were taken from animals at 3.5 and 6 months following infection and dissected into various regions. RNA isolated from these regions was then tested by RNA PCR. It was found that the thalamus was the most common site of viral transcript. All animals, however, were positive in at least two of the regions tested for both gag and env sequences of HIV-1. In other experiments, the immune responses to tetanus toxoid and BCG were tested in rabbits that had been infected with HIV-1. Various protocols were tried and only one produced significant evidence for immune suppression. Animals that were immunized and one week later infected with HIV-1 had significantly diminished humoral and cellular responses. The cellular responses were measured by skin tests and by lung granulomatosis index following sacrifice 6 months after immunization.